1. Field of the Invention
The invention relates generally to equalizing flapper type valves that are used, for example, as subsurface safety valves.
2. Description of the Related Art
Wellbores often include subsurface safety valves used to close off a section of production tubing in the event of an emergency. Flapper valve assemblies have long been employed as safety valves. Flapper valve assemblies typically consist of a curved metal valve member that is shaped to seat upon an annular valve seat within the tubing flowbore to block fluid flow through the flowbore. The valve member is hingedly attached to the inside of the tubing and rotates about the hinge point between open and closed positions. A closed flapper valve is usually opened by an axially shiftable actuation sleeve that contacts the downstream face of the flapper valve and urges the valve member toward its open position. It is, however, difficult to open a flapper valve that has been closed by a high pressure differential. The fluid pressure holding the valve member in the closed position can be very difficult to overcome. It is, therefore, necessary to reduce (i.e., equalize) the pressure differential prior to opening the flapper. This may be done by incorporating an equalizing, or bleed, valve assembly into the flapper valve member.
Prior art equalizing flapper valves of this type are known. U.S. Pat. No. 4,478,286 issued to Fineberg and U.S. Pat. No. 6,644,408 issued to Ives are two examples of equalizing valves. Both of these patents are owned by the assignee of the present invention and both are incorporated herein by reference. Both patents describe flapper valve assemblies that have poppet-type equalizing valves retained therein to bleed off pressure from the upstream side of the flapper valve prior to opening the flapper valve assembly. While effective, these valve assemblies may not be well suited to high slam rate applications where the dynamic forces are so significant that they can damage the equalization valve element during closing (i.e., slamming) of the flapper. A particular problem that has been observed with prior art equalization valve assemblies is that the poppet valve components for the equalization valve assembly can be damaged as the flapper is slammed closed by fluid flow. As a result, the flapper may be unable to fully close off fluid flow as it is intended to do.
U.S. Pat. No. 6,296,061 issued to Leismer describes an equalization flapper device that uses a pilot activator located within a pilot bore and retained in place only by a hinge spring. U.S. Pat. No. 6,079,497 issued to Johnston et al. describes an equalization flapper assembly having a retention member that is formed from a cantilevered beam. Neither of these arrangements is sufficiently robust to effectively resist potential damage during high slam rate applications. Additionally, a cantilevered beam may be unsuitable for effectively biasing closed the equalizing valve because the beam member may not have adequate shape memory, in the manner that a compression spring would have. As a result, the equalizing port may not be fully closed in the absence of a significant pressure differential and may tend to leak fluid in any event.
A related problem with conventional equalizing flapper assemblies stems from damage caused to the upper (downstream) face of the flapper valve member from contact by the actuating sleeve. The axial faces of flapper valve members are curved and shaped as a natural consequence of forming the valve member to generally conform to the surrounding flow tube while in an open position. When a smaller, curved area of metal contacts the lower end of the actuating sleeve, the forces necessary to open the flapper element often deform the metal of the flapper element. Because the equalization valve is normally aligned with the lower end of the actuating sleeve, deformed metal can flow onto the equalization valve member itself, causing the valve member to become non-functional.
The present invention addresses the problems of the prior art.